A. Technical Field
The present invention relates generally to integrated circuits, and more particularly to methods, systems and devices of employing a monitor detection module in a computer or computer system to detect the presence of a VGA display. The monitor detection module takes advantage of synchronization pulses in a horizontal or vertical sync signal to monitor termination resistance of an analog video signal line, and thus, the VGA monitor may be detected reliably at a fast rate while not interfering with video signal transmission.
B. Background of the Invention
Video Graphic Array (VGA) refers to the display hardware first introduced by IBM in 1987, and thereafter, has been widely adopted as an analog display standard by personal computers, e.g., desktop, laptop and tablet computers. A VGA monitor or projector may be employed not only as a primary display device but also as a secondary display device in these personal computers.
In today's computer systems, a software operating system (OS), e.g., Microsoft Windows®, detects and identifies each VGA monitor or projector that is connected, and applies the video settings that are best suited to the display. The software OS collects the display's video capabilities, including screen size, resolution and color depth, and allows a user to choose the video settings when a particular VGA monitor or projector is connected for the first time. These video capabilities and settings are stored in the computer systems, and automatically loaded to configure graphics hardware, e.g., a graphics processing unit (GPU), at the computer-display interface for reconnection of this VGA monitor or projector.
Display data channels (DDC) are formed according to communication protocols between a graphics hardware in the computer system and the VGA monitor. DDC1 and DDC2 are two commonly-used data protocols for integrating digital interfaces in the computer and for enabling communication between the computer and the VGA monitor. DDC1 allows the VGA monitor to send the computer its video settings, and DDC2 allows a bidirectional communication via which the computer not only receives the video settings of the VGA monitor but also controls the video settings. In particular, the signals in DDC2 are consistent with the standard inter-integrated circuit (12C) interface. The software operating systems receive the video settings and/or generate commands to adjust the video settings according to the DDC data protocols.
Despite of acceptable performance in most cases, software-dependent monitor control is plagued with reliability issues. Software needs to issue commands to read or adjust the video settings, and commands are issued via serial data at a relatively low rate. In many occasions, the computer may not detect the VGA monitor right upon connection, and sometimes, may even fail to detect the connection. The software operating system normally has to reserve an option for the users to initialize a manual search for the VGA display. Sometimes, the software operating system checks the monitor load at such a low rate (e.g., once every few minutes) that the computer may not even be aware that a first monitor is disconnected and a second monitor is connected. The video settings of the first monitor may be erroneously adopted by the computer to drive the second monitor. Moreover, the software operating system often fails to detect that a VGA monitor is powered off although it is still connected to the graphics hardware of the computer.
Software-dependent monitor control is also plagued with energy and cost efficiency problems that are associated with some of the aforementioned reliability issues. In particular, when the software operating system neglects the VGA monitor that is powered off, the graphics hardware remains functioning as if the VGA monitor is actively loaded. As a result, the graphics hardware consumes redundant power, which is not desirable as energy requirements get stringent for future products. Moreover, additional filtering components are needed for the graphics hardware in order to reduce noise introduced by an inactive load of the VGA monitor. Cost efficiency is largely degraded due to material and assembly cost. As a result, it is desirable to detect the presence or absence of the VGA monitors reliably at a fast rate, and, more importantly, to detect an inactive connection of the VGA monitor while it is powered off.